Inhibition of human bone marrow-granulocyte precursors by serum from patients with Felty's syndrome.

Eight of 19 patients with Felty's syndrome were shown to have a serum factor capable of inhibiting in vitro colony formation by human bone marrow-granulocyte precursors. These data raise the possibility that a serum factor may play a role in the induction of leukopenia in Felty's syndrome.